Systems for the retention and stabilization of soil and soil-like materials exist in many forms and are utilized in a wide variety of circumstances including as earth retaining walls, bridge abutments, materials storage areas, and the like.
While such retaining systems can use a variety of materials, for larger systems as herein contemplated the structures are normally formed of reinforced concrete, either poured in situ as a unitary structure, or, preferably, formed of an assemblage of stacked precast reinforced concrete blocks or panels with soil reinforcements.
Many efforts have been directed toward improving various aspects of such soil retaining systems, as evidenced by continuing patent activity in this area.
In the known systems, the panels which form the face of the wall are usually quite massive and are provided with configured edges to mate with the edges of adjacent panels to define a positive interlock therewith in an effort to resist relative movement therebetween. The actual configurations of the known panels, normally rectangular or hexagonal, are primarily a function of the ease with which the panel can be formed, handled and stacked. The panels, particularly with walls of any appreciable height, are provided with anchoring systems which engage the panel, for example through connectors embedded within the panel, and extend rearwardly therefrom for embedment within the backfill soil. Such anchoring systems can comprise flat strips of steel or mats of reinforcing rods or wire, precast concrete stems, and the like.
The walls, including the bulk of the panels, the reinforcement therein, the strength of the edge interlock between the panels, and the strength of the soil embedded reinforcement or anchoring system are normally engineered in accord with the anticipated soil load to be retained. This in turn frequently requires specialized design considerations for different projects, with the ultimate goal being to produce a solid wall providing an immovable barrier to earth movement. Any potential for possible shifting of the wall or panels thereof is in most cases avoided by over designing. Notwithstanding the care taken, it is not unknown for cracks or fracture lines to form. Such fracture lines will normally be seen to occur on generally diagonal lines crossing panels themselves and/or following a generally jagged path through selective edge joiners. Such fractures, and the bulk of the loads developed on the formed wall normally result from the natural shrinkage, consolidation and settling of the backfill soil and closely follow the shear planes for a soil in the Rankine passive state.
The Rankine Theory, developed over 100 years ago and well known, basically states that the shear planes for a body of cohesionless soil in a passive state of plastic equilibrium, that is with every part undergoing shrinkage and on verge of failure, will extend at an angle of 45.degree.-.phi./2. The angle of internal friction of a soil is called .phi.. The backfill soils used in these structures are cohesionless and have a .phi. angle that varies from 28.degree. to 34.degree.. Therefore shear plane angles for the backfill soils in the passive state range from 31.degree. to 28.degree.. It is the presence of these shear planes, and the potential for wall failure that result therefrom, that heretofore have been accommodated as above described by the use of massive wall systems and without particular regard to the actual nature of the stresses introduced into the wall.